When a country decides to convert its analogue television network to a digital television, the use of digital receiver is necessary to convert the digital signal to an analogue signal suitable for the television not having the capability to decode the digital signal. A digital receiver can also be used with a digital television, the digital receiver or STB can provide additional services such as EPG or storage not proposed by the digital television.
In order to ease this transition, the cost of the digital converter is in full or part taken by the television provider. This is why this television provider should ensure that the digital converter is only use in connection with the reception of signals broadcasted by this provider.
DVB compliant digital converter (STB) may be used on any DVB network for displaying Free-To-Air services (no dependency on the Conditional Access System, DVB was designed for this). For some reasons, the provider (for example, he subsidized STB and it has a value for him), may want to restrict the usage of these STBs to its network only including also Free-To-Air services.
Since Free-To-Air services are (by definition) not scrambled (no need to use the Conditional Access system to access audio/video services), the Conditional Access systems cannot enforce this usage restriction.